The invention relates to new compounds that are adjacent homologues of known compounds which have been employed as fire retardants in thermoplastics. These known compounds, halogenated phenyl benzyl ethers, are described by Sauer et al. in U.S. Pat. No. 3,250,739. These compounds differ from those of the present invention by only an .alpha.-methyl group. Yet this difference gives the compounds of the invention an unexpected advantage as a fire retardant.
As a general rule, compounds become more suited to use as fire retardants by the addition of more halogen. The present invention, however, adapts a known compound of the art, the halogenated benzyl phenyl ether, to use as a fire retardant by adding more hydrocarbon. Since hydrocarbon lends more fuel for the fire, it would be expected that the compounds of the invention containing similar amounts of halogen would be inferior to the known compounds described by Sauer et al. This, however, is not true. As shown by the comparative examples in the Specific Embodiments, the compounds of the invention act more efficiently as a fire retardant in thermoplastic substrates.
In the search for a suitable fire retardant for thermoplastics, it has been discovered that some samples of a thermoplastic containing a fire retardant behave differently in a low temperature flame, such as that of a paper match, than they do in a high temperature flame, such as that of a Bunsen burner. The ability of fire retardants to act in low temperature flames is very important for most sources of flame which cause significant fire hazards are low temperature flames. Thus, a desirable fire retardant must be efficient in extinguishing a low temperature flame while at the same time providing adequate protection against high temperature flames.